/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.dolphinscheduler.plugin.registry.etcd;

import org.apache.dolphinscheduler.registry.api.ConnectionListener;
import org.apache.dolphinscheduler.registry.api.ConnectionState;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import com.google.common.util.concurrent.ThreadFactoryBuilder;

import io.etcd.jetcd.Client;

public class EtcdConnectionStateListener implements AutoCloseable {
  private final List<ConnectionListener> connectionListeners = Collections.synchronizedList(new ArrayList<>());
  // A thread pool that periodically obtains connection status
  private final ScheduledExecutorService scheduledExecutorService;
  // monitored client
  private final Client client;
  // The state of the last monitor
  private volatile ConnectionState connectionState;

  public EtcdConnectionStateListener(Client client) {
    this.client = client;
    this.scheduledExecutorService = Executors.newScheduledThreadPool(
        1,
        new ThreadFactoryBuilder().setNameFormat("EtcdConnectionStateListenerThread").setDaemon(true).build());
  }

  public void addConnectionListener(ConnectionListener connectionListener) {
    connectionListeners.add(connectionListener);
  }

  @Override
  public void close() throws Exception {
    connectionListeners.clear();
    scheduledExecutorService.shutdownNow();
  }

  /**
   * Apply for a lease through the client, if there is no exception, the connection is normal
   *
   * @return the current connection state
   * @throws if there is an exception, return is DISCONNECTED
   */
  private ConnectionState currentConnectivityState() {
    try {
      client.getLeaseClient().grant(1).get().getID();
      return ConnectionState.CONNECTED;
    } catch (ExecutionException e) {
      return ConnectionState.DISCONNECTED;
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
      return ConnectionState.DISCONNECTED;
    }
  }

  /**
   * Periodically execute thread to get connection status
   */
  public void start() {
    long initialDelay = 500L;
    long delay = 500L;
    this.scheduledExecutorService.scheduleWithFixedDelay(() -> {
          ConnectionState currentConnectionState = currentConnectivityState();
          if (currentConnectionState == connectionState) {
            return;
          }
          if (connectionState == ConnectionState.CONNECTED) {
            if (currentConnectionState == ConnectionState.DISCONNECTED) {
              connectionState = ConnectionState.DISCONNECTED;
              triggerListener(ConnectionState.DISCONNECTED);
            }
          } else if (connectionState == ConnectionState.DISCONNECTED) {
            if (currentConnectionState == ConnectionState.CONNECTED) {
              connectionState = ConnectionState.CONNECTED;
              triggerListener(ConnectionState.RECONNECTED);
            }
          } else if (connectionState == null) {
            connectionState = currentConnectionState;
            triggerListener(connectionState);
          }
        },
        initialDelay,
        delay,
        TimeUnit.MILLISECONDS);
  }

  // notify all listeners
  private void triggerListener(ConnectionState connectionState) {
    for (ConnectionListener connectionListener : connectionListeners) {
      connectionListener.onUpdate(connectionState);
    }
  }
}
